It’s a generally acknowledged truism in sewing, that before ever setting scissor to fabric, one should wash and iron your fabric. There are a multitude of reasons for this necessity. Sometimes fabric has been sitting for long times untouched, so that it is dust covered. Also, if it’s been sitting for a long time, the fabric can stretch a bit over the bolt. Washing it allows the original weave to settle back in to place. Washing it will allow any shrinkage that is going to occur, to happen BEFORE you make to measure. So if you DON’T pre-wash your fabric, there is a very real risk that after you make your fabulous garment, it will shrink with the first wash, thereby becoming unwearable to you.
So this is one of the aphorisms Mary Brooks Picken goes over in Woman’s Institute Library of Dressmaking. She also covers the importance of accurate measurements. This isn’t just in measuring yourself, although that is definitely important. But also in measuring your pattern pieces. Bad measurements create a fitting nightmare. So accuracy in measurements and pre-treating your fabric are two essential elements to good tailoring.